Field of the Invention
The present invention is directed in general to field of capacitive sensor devices. In one aspect, the present invention relates to a touch button keypad topology and keypad sense method, apparatus and system for determining the location of an object on a touch button keypad having a capacitive touch button keypad.
Description of the Related Art
Capacitive sensor devices are increasingly used to capture user input in a variety of electronic devices (e.g., cellular telephones, appliances, industrial equipment, MP3players, personal digital assistants (PDAs), tablet computers and other similar portable electronic devices) and automotive applications (e.g., car steering wheel control buttons, HVAC control panel, overhead console, etc.). Examples of such capacitive sensor devices include touch button keypads which use capacitive keypads or buttons to sense user touch inputs to provide data input for one or more applications. Touch button keypads have advantages over conventional input keypads because they do not have complex mechanical parts that can be expensive to manufacture and can wear out or break and because they can be completely sealed to the external environmental conditions that can degrade the contacts or get inside the product provoking malfunctions. To capture user input, touch button keypads typically employ capacitive keypads in which each keypad is configured as an electrode which functions as a capacitor plate to interact with a second “plate” formed by the human touch or other input device to measure a touch voltage which is converted into digital form by an analog-to-digital converter (ADC), thereby enabling detection of a change in a signal due to capacitive coupling created by a touch on the touch panel. In operation, an electric field that is applied to electrodes below the touch panel is changed or altered in the vicinity of a detected touch because the touch capacitively couples with the electrode(s). The change in the field is detected and used to determine the touch location. With touch panel designs, there a number of disadvantages associated with conventional approaches, particularly in relation to the computational requirements, and power consumption associated with accurately monitoring and sensing multiple, different keypad electrodes. As seen from the foregoing, the existing capacitive touch button keypad solutions are extremely difficult at a practical level by virtue of the difficulty in accurately and efficiently capturing keypad inputs, especially with keypads employing multiple capacitor electrodes which require increased computation support and power consumption while introducing measurement inaccuracies due to process variations associated with the fabrication and measurement of capacitor electrodes.